Aeronautical Information Manual (AIM), page 87

Index   86 -- Page 87 -- 88

2. LAAS was developed as an "ILS look-alike"
system from the pilot perspective. LAAS is based on
GPS signals augmented by ground equipment and has
been developed to provide GLS precision approaches
similar to ILS at airfields.

3. GLS provides guidance similar to ILS

approaches for the final approach segment; portions
of the GLS approach prior to and after the final
approach segment will be based on Area Navigation
(RNAV) or Required Navigation Performance
4. The equipment consists of a GBAS Ground
Facility (GGF), four reference stations, a VHF Data
Broadcast (VDB) uplink antenna, and an aircraft
GBAS receiver.

b. Procedure
1. Pilots will select the five digit GBAS channel
number of the associated approach within the Flight
Management System (FMS) menu or manually select
the five digits (system dependent). Selection of the
GBAS channel number also tunes the VDB.
2. Following procedure selection, confirmation
that the correct LAAS procedure is loaded can be
accomplished by cross checking the charted
Reference Path Indicator (RPI) or approach ID with
the cockpit displayed RPI or audio identification of
the RPI with Morse Code (for some systems).

3. The pilot will fly the GLS approach using the
same techniques as an ILS, once selected and

1-1-20. Precision Approach Systems other
than ILS and GLS

a. General
Approval and use of precision approach systems
other than ILS and GLS require the issuance of
special instrument approach procedures.
b. Special Instrument Approach Procedure

1. Special instrument approach procedures

must be issued to the aircraft operator if pilot training,

aircraft equipment, and/or aircraft performance is

different than published procedures. Special instru-
ment approach procedures are not distributed for
general public use. These procedures are issued to an
aircraft operator when the conditions for operations
approval are satisfied.

2. General aviation operators requesting ap-
proval for special procedures should contact the local
Flight Standards District Office to obtain a letter of
authorization. Air carrier operators requesting
approval for use of special procedures should contact
their Certificate Holding District Office for authoriz-

ation through their Operations Specification.

c. Transponder Landing System (TLS)
1. The TLS is designed to provide approach
guidance utilizing existing airborne ILS localizer,
glide slope, and transponder equipment.
2. Ground equipment consists of a transponder
interrogator, sensor arrays to detect lateral and
vertical position, and ILS frequency transmitters. The
TLS detects the aircraft's position by interrogating its
transponder. It then broadcasts ILS frequency signals
to guide the aircraft along the desired approach path.
3. TLS instrument approach procedures are
designated Special Instrument Approach Procedures.
Special aircrew training is required. TLS ground
equipment provides approach guidance for only one
aircraft at a time. Even though the TLS signal is
received using the ILS receiver, no fixed course or
glidepath is generated. The concept of operation is
very similar to an air traffic controller providing radar
vectors, and just as with radar vectors, the guidance
is valid only for the intended aircraft. The TLS
ground equipment tracks one aircraft, based on its
transponder code, and provides correction signals to
course and glidepath based on the position of the
tracked aircraft. Flying the TLS corrections com-
puted for another aircraft will not provide guidance
relative to the approach; therefore, aircrews must not
use the TLS signal for navigation unless they have
received approach clearance and completed the
required coordination with the TLS ground equip-
ment operator. Navigation fixes based on
conventional NAVAIDs or GPS are provided in the
special instrument approach procedure to allow
aircrews to verify the TLS guidance.
d. Special Category I Differential GPS (SCAT-

1. The SCAT-I DGPS is designed to provide

approach guidance by broadcasting differential

correction to GPS.

2. SCAT-I DGPS procedures require aircraft
equipment and pilot training.
3. Ground equipment consists of GPS receivers
and a VHF digital radio transmitter. The SCAT-I

Navigation Aids 1-1-33

Page 87 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   86 -- Page 87 -- 88